With many concerned about the return to power of his Institutional Revolutionary Party, Peña Nieto pledges to listen to divergent views while addressing the nation's violence and poverty.

MEXICO CITY — Enrique Peña Nieto, a 46-year-old career politician and member of Mexico's old-guard political party, Saturday assumed the presidency of a nation reeling from drug-related violence, promising his fellow citizens that "the primary focus of my government is to achieve a Mexico at peace."

By that measure, his term did not start well. Outside the lower house of Congress, where Peña Nieto was given the presidential sash by his predecessor, Felipe Calderon, protesters clashed with police, lobbing Molotov cocktails and rocks. Authorities responded with tear gas and rubber bullets. A number of police officers and protesters were injured, some of them seriously, officials said.

Many of the demonstrators were left-leaning students and activists concerned about the return to power of Peña Nieto's Institutional Revolutionary Party, or PRI, which ruled Mexico as a virtual one-party state for much of the 20th century, often by less than democratic means.

"Peña Nieto, the people hate you," read one graffito on scrawled on the heavy fortifications surrounding Congress.

But in a later speech in an elegant courtyard of Mexico's National Palace, Peña Nieto pledged to respect the social and governmental forces, from opposition lawmakers to a more aggressive national media, that will attempt to keep any authoritarian tendencies on the part of the PRI in check in the coming years.

"I will respect each and every one of the voices of society," he said. "Mine will be a facilitating government, carrying out the best ideas of Mexicans. I'll be a president close to the people. I will travel the country accompanied by the members of my Cabinet."

Street protests probably will be the least of Peña Nieto's problems. The goal of peace famously eluded Calderon of the conservative National Action Party, or PAN, throughout his six-year term. He decided to launch an assault against the nation's powerful drug cartels shortly after his own inauguration. Tens of thousands died in the crackdown. But the cartels remained, and the flow of drugs to the U.S. was not impeded.

As a result, the new president inherits a troubled nation deeply divided about how to proceed with its drug war: A recent poll showed that 51% of respondents wanted the government to negotiate with the drug cartels, while 49% said the government should continue to challenge them with arms.

On Saturday, Peña Nieto did little to clarify his internal security strategy, which he previously had said would focus on violent crimes such as murder and extortion that affect the everyday lives of Mexicans.

But he was candid in describing the twin failures of violence and inequality that have hurt Mexico's international reputation and quality of life, even as the country has benefited in recent years from a stable economy and increasingly mature democratic institutions.

"Mexico hasn't achieved the advances that its population demands and deserves," he told an audience that included Vice President Joe Biden. "Insecurity and violence have robbed peace and liberty from various communities in our national territory."

The PRI has sought to present itself as a more democratic entity since 2000, when the election of PAN candidate Vicente Fox ended its 71-year grip on power. It is a party with no true North American analogue, with a tent big enough to contain both free-market conservative "neoliberals" and devout leftists.

As a candidate, Peña Nieto, rather typical of a PRI member, presented himself not as an ideologue, but as a practical problem-solver. He received about 38% of the vote in July, defeating a pair of candidates from more traditionally defined left- and right-wing parties.

On Saturday, however, Peña Nieto struck a decidedly populist tone on the subject of poverty, which, according to government figures, increased to 46% from 43% at the beginning of Calderon's term.

"We are a nation that is growing at two speeds," he said. "There's a Mexico of progress and development. But there's another one that lives in sluggishness and poverty."

An "inclusive Mexico," he said, would be the second major focus of his single, six-year term, to which all presidents are limited by the Mexican Constitution. "We need to be a society of the middle class, with cohesion and equality of opportunity," he said.

The early afternoon speech was smoothly delivered by a politician known more for his unflappable public presence and telegenic good looks than for his intellectual heft (on the campaign trail he struggled to name his three favorite books). Invited guests applauded politely. At the earlier ceremony, however, in which Peña Nieto received the presidential sash, leftist politicians hoisted a huge black banner that declared "Mexico in Mourning," a reference to those killed during Calderon's term.

It also, most likely, was an expression of frustration that Peña Nieto has pledged to maintain two key components of Calderon's security strategy: using the military to keep the peace and continuing the intimate partnership with the United States, which took on an unprecedented role in Mexican internal affairs during the Calderon era.